Solid inorganic insulation for metallic conductors



Oct. 16, 1962 D. c. WESTERVELT ETAL 3,059,046

SOLID INORGANIC INSULATION FOR METALLIC CONDUCTORS Filed May 16, 1958 Fig. I.

Fibrous Insulation lmpregnoied with Inorganic Insulation WITNESSES= INVENTORS Deon C.Westervelt, Charles H.Vondrc|cek W2. and Charles Ho cinn.

United States Patent ()fifice Patented Oct. 16, 1962' 3,059,046 SOLID INORGANIC INSULATION FOR METALLlC CQNDUCTORS Dean C. Westervelt, Pitcairn, Charles H. Vondracek, Wilkins Township, Allegheny County, and Charles F. Hofmann, Monroeville, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed May 16, 1958, Ser. No. 735,891 6 Claims. (Cl. 174110) The present invention relates to coating compositions and has particular reference to electrical metallic conductors provided with heat-hardened, solid, inorganic insulation adapted for use at temperatures up to 500 C.

Coatings on metallic conductors such as wires must be tough and hard to withstand the severe mechanical abuse to which the windings are subjected in service. Thus, coils frequently are wound from insulated wire under considerable pressure and at high speeds. It is essential that the insulating coating applied to the wire be capable of withstanding the abrasion, bending stresses, and heavy pressures encountered during such winding without breaking, cracking or otherwise disrupting from the wire.

Organic enameling compositions are used widely in the electrical industry to provide insulation for metallic conductors such as wires. In general, such organic coatings are not capable of operating satisfactorily for pro-longed periods of time at temperatures substantially above 200 C. There is a need in the electrical industry for a Wire coating composition which, after application and when hardened on the wire, will operate satisfactorily for relatively long periods of time at temperatures of 500 C. and higher.

The surprising discovery has now been made that fluid inorganic compositions containing an aluminum compound, phosphoric acid, and a finely divided filler may be applied conveniently to metallic conductors such as wires and thereafter dried to provide a wire with a flexible coating which adheres tenaciously thereto. This wire may be wound on spools and stored. When ready for use, it may be wound into coils or the like and baked to provide members having non-flexible durable, tough, hard insulating coatings which will function satisfactorily at temperatures of 500 C. and higher.

The object of the present invention is to provide metallic electrical conductors insulated with a heat-hardened inorganic coating composition comprising (1) an aluminum compound, (2) phosphoric acid, and (3) a finely divided filler.

Another object of the invention is to provide electrically conducting wires provided with a layer of inorganic fibrous material and a tough, durable, insulating composition impregnated into at least a portion of the fibrous material, the composition comprising a heat converted fluid inorganic composition comprising (1) an aluminum compound, (2) phosphoric acid, and (3) a finely divided filler.

Still another object of this invention is to provide metallic electrical conductors provided with a dry-appearing coating having a moisture content of from 5% to 20%, the coating comprising (1) an aluminum compound, (2) phosphoric acid, and (3) a finely divided filler.

Other and further objects of the invention will, in part, be obvious and will, in part, appear hereinafter.

For a more complete understanding of the present invention, reference is made to the following description taken in conjunction with the accompanying drawing.

wherein:

FIGURE 1 is a fragmentary isometric view of a metallic conductor provided with a coating composition of this invention; and I FIG. 2 is a cross-sectional view of a metallic conductor insulated with fibrous material impregnated With a coating composition of this invention.

Broadly, in the attainment of the foregoing objects and in accordance with the present invention there is provided a metallic conductor insulated with a heat c011- verted inorganic composition comprising (A) from 90 to 20 parts by weight of an aqueous mixture consisting of (a) from 10% to 40% by weight of aluminum phosphate, (b) from 10% to 40% by weight of phosphoric acid, (0) the balance water, and (B) from 10 to parts by weight of a certain solid inorganic particulate filler to be described more fully hereinafter.

In preparing the insulated conductors of this invention, a liquid suspension comprising a mixture of components identified above as (A) and (B) first are applied to the conductor and then dried by passing the coated conductor through a wire coating tower at a temperature of from 50 C. to 400 C. for a period of time sufiicient to reduce the moisture content of the coating to about 20% to 5% by weight. The wire with its applied coating of flexible, tightly adhering dried insulating material may be stored indefinitely before use. When ready for use, the wire may be employed in the building or winding of transformers, motors, solenoids, or other electrical equipment. Heating of the coated wire in the form of wound electrical members at a temperature of from 200 C. to 300 C. for about 5 to 60 minutes results in the development of a fully cured, non-flexible insulating coating on the wire permitting satisfactory continuous use of the member at a temperature of 500 C. or higher for a prolonged period of time.

The phosphates employed in this invention are those known as aluminum phosphates. As used in the instant specification and in the appended claims, the term aluminum phosphate refers not only to aluminum phosphate AlPO but also to aluminum mono-hydrogen phosphate Al (l-IPO and to aluminum di-hydrogen phosphate Al(H PO as well as to mixtures of two or more of these.

The aluminum phosphate is employed in the aqueous mixture (A) portion in amounts within the range of about 10% to 40% by weight, with amounts within the range of about 18% to 23% by weight being preferred.

The phosphoric acid employed includes not only orthophosphoric acid of: the formula H PO but also pyro-phosphoric acid having the formula H P O as well as meta-phosphoric acid having the formula HPO The term phosphoric acid as employed in the instant specification and in the present claims includes metaand pyro-phosphoric acids as Well as ortho-phosphoric acid. Phosphoric acid is employed with the aluminum phosphate in the aqueous mixture (A) portion of the herein described liquid impregnating suspension in amounts within the range of about 10% to 40% by weight, preferably in the range of about 27% to 31% by weight of mixture (A). These amounts are based upon ortho-phosphoric acid. When metaand/ or pyrophosphoric acids are used they should be employed, of course, in equivalent amounts.

Satisfactory wire coating compositions suitable for use at temperatures of 500 C. and higher are not obtained employing only an aqueous mixture of aluminum phosphate and phosphoric acid. It is essential that specific solid inorganic particulate fillers also be incorporated in the composition. The importance of these fillers is dephosphoric acid is not fully understood at this time;

However, applied coatings which do not contain the fillers exhibit poor thermal shock resistance and poor mechanical impact resistance. Moreover, in the absence of the inorganic fillers, the coatings become so moisture sensitive that they absorb water whereby the bond between the metallic conductor or wire and the insulating composition is destroyed with the result that the composition crumbles, thereby impairing almost completely the insulating characteristics of the coated conductor.

Inorganic fillers which have been found to be essential for use in combination with the aqueous mixture of aluminum phosphate and phosphoric acid of this invention consist essentially of compounds selected from at least one of the group consisting of the oxides, hydroxides, and silicates of metals selected from the group consisting of calcium, barium, magnesium, cadmium, aluminum, zinc, lead and titanium. These filler compounds may be used singly or in mixtures of any two or more. The filler may be employed in combination with the other components in amounts within the range of from 10 to 80 parts by weight. The particles should have an average size of between and 150 microns, preferably of an average size of from 5 to '75 microns.

The compositions of this invention are particularly useful in coating metallic conductors or wires since the moisture content of the compositions will be reduced to about 5% to 20% in from one to several seconds at temperatures of from 50 C. to 400 C. in a wire-coating tower. The wire with the dried flexible coating adhering thereto then may be wound on spools and stored. When ready for use, for example in winding coils, the wire may be unwound from the spool and wound into a coil of desired configuration. The wound coil then may be baked at from 200 C. to 300 C. until the coating is converted to a hard, tough non-flexible insulating coating.

The phenomenon of rapid drying in the tower occurs only when the particular metal oxide, hydroxide, and silicate fillers herein described are employed in combination with the water mixture of aluminum phosphate and phosphoric acid. The rate at which a given composition will dry depends upon the particular filler used, the amount of filler, and its particle size. In general, the more filler used and the smaller its particle size the faster the composition will harden. Moreover, the metal oxides bring about a faster hardening rate than do the metal silicates.

In order to illustrate this invention even more fully, the following specific examples are set forth: The parts and percentages given are all by weight unless otherwise indicated.

Example I A No. 17 A.W.G. copper wire is passed through a liquid suspension containing 35 parts of calcium silicate having an average particle size of about fifty microns and 65 parts by weight of an aqueous mixture containing 20% of aluminum phosphate, 20% ortho-phosphoric acid, and the balance water. The wire was passed through a coating tower maintained at a temperature of from 200 C. to 250 C. at a rate sufficient to reduce the moisture content in the coating to about 15%. The coating then was dry to the touch and flexible. The insulated wire was wound into a coil and baked seventy-five minutes at 250 C. The insulation on the wire of this coil was non-flexible and had sufiicient heat stability to permit satisfactory operation of the coil at temperatures as high as 500 C. Moreover, the insulating coating did not chip or break during application of the coating or during winding of the coil.

Example 11 A No. 17 A.W.G. aluminum wire was passed through a liquid suspension comprising (A) 60 parts of an aqueous mixture containing (a) 15% of aluminum di-hydrogen phosphate and (b) 15% of pyro-phosphoric acid, and (c) 70% water, and (B) 40 parts of a finely divided filler made up of 5 parts of magnesium oxide and 35 parts aluminum silicate. The coated wire was passed through a wire coating tower maintained at a temperature of 200 C. at a rate whereby the moisture content of the coating was reduced to about 10%. The coating then was flexible on the wire and dry to the touch. After several weeks storage, this coated wire was wound into a solenoid coil. The coil then was baked for twenty-five minutes at 300 C. whereby the coating was converted to non-flexible, tough, hard insulation. The insulating coating did not crack nor break during winding of the coil.

Example III The following materials were mixed in a suitable vessel:

Percent Aluminum phosphate 20 Phosphoric acid 30 Water 50 A wire coating composition was prepared by addition to sixty-five parts of this mixture, 12 parts of aluminum oxide and twenty-three parts of mica. The resultant composition when applied to wire and dried and baked provided a tough solid electrical insulation for the wire.

Referring to FIG. 1 of the drawing, there is illustrated a conductor 10 comprising a copper Wire 12 coated with a hard, tough, solid inorganic insulating coating 14 produced by applying the liquid coating composition of this invention thereto and drying and curing the same. It will be understood that the coating 14 may be applied by any suitable means, such as by dipping, die-coating, or the like. nickel, copper, aluminum, silver, either alone or as plated or clad combinations or alloys, as well as nickel-chromium alloys, stainless steel alloys, anodized aluminum, or the like. While conductor 12 is illustrated as being circular in cross-section, it will be understood that it may be of any other desirable cross-section such as rectangular, square, fiat strip, foil, or the like.

The coatings of this invention also may be applied to electrical conductors such as wire in combination with coatings of inorganic fibrous materials. One form of such a modification is illustrated in FIG. 2. A copper wire 16 is provided with an exterior coating 18 of a fibrous material which may comprise glass cloth, glass paper, glass mat, asbestos cloth, asbestos paper, asbestos mat, quartz paper, and the like. The fibrous material may be wrapped, braided, or woven or various combinations thereof. A quantity of coating composition 20 of this invention is impregnated into at least a part of the inorganic fibrous material 18 and cured to provide a composite solid insulation on wire 16.

Fillers other than the oxides and silicates disclosed hereinabove also may be incorporated in the coating compositions of this invention in amounts up to about 30% by weight. Pigments and dyes also may be added as desired. Examples of additional fillers include mica, silica, and the like. These fillers should be used in finely divided form and they may be employed singly or in combinations of two or more.

While this invention has been described with reference to what are presently considered to be preferred embodiments thereof, it will be understood, of course, that certain changes, substitutions, modifications and the like may be made therein without departing from its true scope.

We claim as our invention:

1. An insulated electrical conductor comprising, in combination, a metallic conductor and an insulating coating applied to the metallic conductor, the coating having been derived by applying to the conductor a liquid suspension comprising, (A) from to 20 parts by weight of an aqueous mixture consisting of (a) from 10% to 40% by weight of aluminum phosphate, (b) from 10% Conductor 10 may be of a metal such as to 40% by Weight of phosphoric acid, and (c) the balance water, and (B) from 10 to 80 parts by weight of a solid inorganic particulate filler comprising oxides, hydroxides, and silicates of metals selected from the group consisting of calcium, barium, magnesium, cadmium, aluminum, zinc, lead, and titanium, and drying the applied liquid suspension by maintaining it at a temperature of from 50 C. to 400 C. for a period of time sufficient to reduce the moisture content of the suspension to about 5% to 20% by weight and provide an uncured, flexible, tightly-adhering, dry, insulating coating on the conductor.

2. An insulated electrical conductor comprising, in combination, a metallic conductor, a layer of inorganic fibrous material applied to the conductor, and a coating applied to impregnate at least a part of the inorganic fibrous material, the coating having been derived by applying to the fibrous material a liquid suspension comprising, (A) from 9 to 20 parts by weight of an aqueous mixture consisting of (a) from 10% to 40% by weight of aluminum phosphate, (b) from 10% to 40% by weight of phosphoric acid, and (c) the balance water, and (B) from 10 to 80 parts by Weight of a solid inorganic particulate filler comprising oxides, hydroxides, and silicates of metals selected from the group consisting of calcium, barium, magnesium, cadmium, aluminum, zinc, lead, and titanium, and drying the applied liquid suspension by maintaining it at a temperature of from 50 C. to 400 C. for a period of time sufficient to reduce the moisture content of the suspension to about to 20% by weight and provide an uncured, flexible, tightly-adhering, dry, insulating coating on the conductor.

3. Insulated electrical apparatus adapted for use at temperatures as high as 500 C. comprising, in combination, a metallic conductor and a solid insulating coating applied to the conductor, the coating having been derived by applying to the conductor a liquid suspension comprising, (A) from 90 to 20 parts by weight of an aqueous mixture consisting of (a) from to 40% by weight of aluminum phosphate, (12) from 10% to 40% by weight of phosphoric acid, and (c) the balance water and (B) from 10 to 80 parts by weight of a solid inorganic particulate filler comprising oxides, hydroxides, and silicates of metals selected from the group consisting of calcium, barium, magnesium, cadmium, aluminum, zinc, lead, and titanium, and drying the applied liquid suspension by maintaining it at a temperature of from 50 C. to 400 C. for a period of time sufficient to reduce the moisture content of the suspension to about 5% to 20% by weight, and provide an uncured, flexible, tightly-adhering, dry, insulating coating on the conductor, forming the coated conductor to apparatus shape and then heating the dried coating to a temperature of about 350 C. to 500 C. to convert it to fully cured, non-flexible, solid insulation.

4. Insulated electrical apparatus adapted for use at temperatures as high as 500 C. comprising, in combination, a metallic conductor, a layer of inorganic fibrous material applied to the conductor, and a solid insulating coating applied to impregnate at least a part of the inorganic fibrous material, the coating having been derived by applying to the fibrous material a liquid suspension comprising, (A) from 90 to 20 parts by weight of an aqueous mixture consisting of (a) from 10% to 40% by weight of aluminum phosphate, (b) from 10% to 40% by weight of phosphoric acid, and (c) the balance water, and (B) from 10 to 80 parts by weight of a solid inorganic particulate filler comprising oxides, hydroxides, and silicates of metals selected from the group consisting of calcium, barium, magnesium, cadmium, aluminum, zinc,

lead, and titanium, and drying the applied liquid suspension by maintaining it at a temperature of from 50 C. to 400 C. for a period of time suflicient to reduce the moisture content of the suspension to about 5% to 20% by Weight and provide an uncured, flexible, tightly adhering, dry insulating coating on the conductor forming the coated conductor to apparatus shape, and then heating the dried coating to a temperature of about 350 C. to 500 C. to convert it to fully cured, non-flexible, solid insulation.

5. An insulated electrical coil comprising a metallic conductor and an insulating coating applied to the metallic conductor, the coating having been derived by applying to the conductor a liquid suspension comprising, (A) from 90 to 20 parts by weight of an aqueous mixture consisting of (a) from 10% to 40% by Weight of aluminum phosphate, (12) from 10% to 40% by weight of phosphoric acid, and (c) the balance water, and (b) from 10 to parts by weight of a solid inorganic particulate filler comprising oxides, hydroxides, and silicates of metals selected from the group consisting of calcium, barium, magnesium, cadmium, aluminum, zinc, lead, and titanium, and drying the applied liquid suspension by maintaining it at a temperature of from 50 C. to 400 C. for a period of time sufiicient to reduce the moisture content of the suspension to about 5% to 20% by weight and provide an essentially uncured, flexible, tightly-adhering, dry, insulating coating on the conductor, winding the coated conductor into the coil form and then heating the dried coating to a temperature of about 300 C. to

insulation.

6. An insulated electrical coil comprising, in combination, a metallic conductor, a layer of inorganic fibrous material applied to the conductor and a solid insulating coating applied to impregnate at least a part of the inorganic fibrous material, the coating having been derived by applying to the fibrous material a liquid suspension comprising, (A) from to 20 parts by Weight of an aqueous mixture consisting of (a) from 10% to 40% by weight of aluminum phosphate, (1)) from 10% to 40% by weight of phosphoric acid, and (c) the balance Water, and (B) from 10 to 80 parts by weight of a solid inorganic particulate filler comprising oxides, hydroxides, and silicates of metals selected from the group consisting of calcium, barium, magnesium, cadmium, aluminum, zinc, lead, and titanium, and drying the applied liquid suspension by maintaining it at a temperature of from 50 C. to 400 C. for a period of time suflicient to reduce the moisture content of the suspension to about 5% to 20% by weight, and provide an essentially uncured, flexible, tightly-adhering, dry insulating coating on the conductor, winding the coated conductor into coiled form and then heating the dried coating to a temperature of about 350 C. to 500 C. to convert it to fully cured, non-flexible, solid insulation.

References Cited in the file of this patent UNITED STATES PATENTS 1,828,211 Wolfsholz Oct. 20, 1931 2,233,700 Grossman Mar. 4, 1941 2,455,758 Greger Dec. 7, 1948 2,504,764 Vollrath Apr. 18, 1950 2,687,967 Yedlick Aug. 31, 1954 2,888,406 Bondley et al. v May 26, 1959 FOREIGN PATENTS 513,030 Great Britain 1939 

3. INSULATED ELECTRICAL APPARATUS ADAPTED FOR USE AT TEMPERATURES AS HIGH AS 500*C. COMPRISING, IN COMBINATION, A METALLIC CONDUCTOR AND A SOLID INSULATING COATING APPLIED TO THE CONDUCTOR, THE COATING HAVING BEEN DERIVED BY APPLYING TO THE CONDUCTOR A LIQUID SUSPENSION COMPRISING, (A) FROM 90 TO 20 PARTS BY WEIGHT OF AN AQUEOUS MIXTURE CONSISTING OF (A) FROM 10% TO 40% BY WEIGHT OF ALUMINUM PHOSPHATE, (B) FROM 10% TO 40% BY WEIGHT OF PHOSPHORIC ACID, AND (C) THE BALANCE WATER AND (B) FROM 10 TO 80 PARTS BY WEIGHT OF A SOLID INORGANIC PARTICULATE FILLER COMPRISING OXIDES, HYDROXIDES, AND SILICATES OF METALS SELECTED FROM THE GROUP CONSISTING OF CALCIUM, BARIUM, MAGNESIUM, CADMIUM, ALUMINUM, ZINC, LEAD, AND TITANIUM, AND DRYING THE APPLIED LIQUID SUSPENSION BY MAINTAINING IT AT A TEMPERATURE OF FROM 50* C. TO 400* FOR A PERIOD OF TIME SUFFICIENT TO REDUCE THE MOISTURE CONTENT OF THE SUSPENSION TO ABOUT 5% TO 20% BY WEIGHT, AND PROVIDE AN INCURED, FLEXIBLE, DTIGHTLY-ADHERING, DRY, INSULATING COATING ON THE CONDUCTOR, FORMING THE COATED CONDUCTOR TO APPARATUS SHPE AND THEN HEATING THE DRIED COATING TO TEMPERTURE OF ABOUT 350* C. TO 500* C. TO CONVERT IT TO FULY CURED, NON-FLEXIBLE, SOLID INSULATION. 